The present invention relates to the pattern inspection technology, and namely, to the technology which is effectively applied to failure inspection for patterns of semiconductor wafers, photomasks, magnetic disks, photo disks and the like, and particuarly to pattern or defect inspection for integrated circuit devices having both period pattern and random pattern in a single chip area of a VLSI memory or a CCD (Charge Coupled Device) or the like.
As a conventional pattern inspection method, a system for comparing two adjacent chips has been heretofore widely used as an appearance inspection apparatus for a photomask or a wafer. In addition, as a defect detection method for a wafer having a complicated multi-layer pattern, a method for repeatedly comparing patterns has been proposed as disclosed in Japanese Patent Application Laid-Open Publication No. 59-192943 (1984).
The two-chip comparison inspection compares patterns of two adjacent chips, and has, in case of a semiconductor wafer having a multilayer pattern, a problem that detection of a minute defect is difficult due to the difference in pattern dimension, overlapping accuracy of patterns and the like by chips. On the other hand, the repeated pattern comparison method compares patterns nearby, and a difference between the patterns compared is small and even a minute defect can be detected, but there is a problem that only the repeated pattern portion can be inspected.
In case of a wafer pattern which is to be inspected, a fine pattern portion is different from a relatively thick pattern in size of an interior defect, and accordingly, the sensitivity of detection required is also different.
Therefore, the present inventors have proposed a method for switching the sensitivity of detection by a pattern to be inspected, as disclosed in Japanese Patent Application Laid-Open Publication 63-52434 (1988).
Furthermore, as an inspection apparatus for carrying out both two-chip comparison and repeated pattern comparison, a Wafer Appearance Inspection Apparatus KLA-20 Series made by KLA limited, U.S.A. has been proposed. According to this apparatus, repeated patterns and random patterns can be separately inspected.